B-Myb-Dependent Regulation of c-Myc Expression by Cytosolic Phospholipase A2

Abstract

Cytosolic phospholipase A2 (cPLA2) cleaves membrane phospholipids to release arachidonic acid, initiating lipoxygenase and cyclooxygenase pathways. Mice lacking a gene for cPLA2 suggested important roles of the protein in allergic responses, fertility, and neural cell death. Here we show that cPLA2 negatively regulates c-Myc expression in a B-Myb-dependent manner. Overexpression of cPLA2 protein but not a mutant cPLA2 protein that lacks in vitro binding ability with B-Myb inhibits B-Myb-dependent c-myc gene expression. The inhibition was associated with physical interaction of B-Myb protein with cPLA2 both in the cytoplasm and the nucleus. Binding site analysis demonstrated that both the N and C termini of cPLA2 interact with B-Myb. Macrophage colony stimulating factor (MCSF) stimulated cPLA2 redistribution into the nucleus and also association with B-Myb in human monocytes. Importantly, macrophages from mice with a disrupted cPLA2 gene demonstrated significantly increased levels of c-Myc protein in the nucleus compared with cells from the wild-type mice, whereas B-Myb levels were similar in the cells from the cPLA2+/+ and cPLA 2-/- mice. Moreover, an introduction of cPLA2 into cPLA2-/- mouse macrophages resulted in decreased c-Myc protein levels, and an inhibition of cPLA2 expression by small interfering RNAs or antisense RNA increased the c-myc transcription in macrophage colony stimulating factor-activated human monocytes. These findings provide new insights into the function of cPLA2 in B-Myb-dependent gene expression.